Graphene pressure sensors
Semiconductor nano pressure sensor devices having graphene membrane suspended over open cavities formed in a semiconductor substrate. A suspended graphene membrane serves as an active electro-mechanical membrane for sensing pressure, which can be made very thin, from about one atomic layer to about 10 atomic layers in thickness, to improve the sensitivity and reliability of a semiconductor pressure sensor device.
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This application is a Continuation of U.S. patent application Ser. No. 13/445,029, filed on Apr. 12, 2012, the disclosure of which is incorporated herein by reference.
TECHNICAL FIELDThe field relates generally to semiconductor nano-devices for sensing pressure and, in particular, semiconductor nano-pressure sensor devices that are constructed using thin graphene membranes.
BACKGROUNDIn general, semiconductor nano pressure sensor devices are used to measure the pressure of gases or liquids, for example, and are utilized in various control and real-time monitoring applications. Semiconductor nano pressure sensor devices can also be utilized to indirectly measure other variables such as fluid flow, gas flow, speed, water level, and altitude, for example. Commonly used pressure sensors implement a strain gauge device with an active membrane that is made of silicon (monocrystalline), a polysilicon thin film, a bonded metal foil, a thick film, or a sputtered thin film, for example. Typically, the thinner the active membrane, the more deformation there will be of the membrane material in response to external pressure, thereby providing higher sensitivity and precision. It is very challenging, however, to produce ultra-thin silicon membrane for use with a pressure sensor device due to the brittle nature of the material.
SUMMARYAspects of the invention include semiconductor nano-devices for sensing pressure and, in particular, semiconductor nano pressure sensor devices that are constructed using thin graphene membranes. A suspended graphene film serves as an active electro-mechanical membrane for sensing pressure, which can be made very thin, from about one atomic layer to about 10 atomic layers in thickness, to greatly improve the sensitivity and reliability of a semiconductor pressure sensor device.
For example, in one aspect of the invention, a semiconductor pressure sensor device includes an insulating layer disposed on a semiconductor substrate, wherein a recessed cavity is formed in the insulating layer. A first graphene membrane is disposed on a surface of the insulating layer completely covering the recessed cavity. A first sense electrode and a second sense electrode are disposed on the insulating layer on opposing sides of, and in contact with, the first graphene membrane. A sealing ring forms a seal around outer sidewalls of the first and second sense electrodes and the first graphene membrane.
In another aspect of the invention, the semiconductor pressure sensor device further includes a second graphene membrane disposed on a surface of the insulating layer in a region adjacent to the first graphene membrane. A third sense electrode and a fourth sense electrode are disposed on the insulating layer on opposing sides of, and in contact with, the second graphene membrane. A second sealing ring forms a seal around outer sidewalls of the third and fourth sense electrodes and the second graphene membrane.
In yet another aspect of the invention, a method of forming a semiconductor pressure sensor device includes forming an insulating layer on a semiconductor substrate, forming a recessed cavity in the insulating layer, forming a first graphene membrane on a surface of the insulating layer completely covering the recessed cavity, forming a first sense electrode and a second sense electrode on the insulating layer on opposing sides of, and in contact with, the first graphene membrane, and forming a sealing ring around outer sidewalls of the first and second sense electrodes and the first graphene membrane.
In another aspect of the invention, the method further includes forming a second graphene membrane on a surface of the insulating layer in a region adjacent to the first graphene membrane, forming a third sense electrode and a fourth sense electrode on the insulating layer on opposing sides of, and in contact with, the second graphene membrane; and forming a second sealing ring around outer sidewalls of the third and fourth sense electrodes and the second graphene membrane.
These and other aspects, features and embodiments of the present invention will become apparent from the following detailed description of preferred embodiments, which is to be read in conjunction with the accompanying figures.
Preferred embodiments of the invention will now be described in further detail with regard to semiconductor nano pressure sensor devices that are constructed using thin graphene membranes. For example,
In general, the graphene membranes 120 and 125 are used to detect pressure of an applied test gas based on changes in resistance of the graphene membranes 120, 125, as will be discussed in further detail below with reference to
The sense electrodes 130 and 131 are used to apply a control voltage across the supported graphene membrane 120 and measure its resistance based on current flowing through the supported graphene membrane 120 between the sense electrodes 130 and 131. Similarly, the sense electrodes 132 and 133 are used to apply a control voltage across the suspended graphene membrane 125 and measure its resistance based on current flowing through the suspended graphene membrane 125 between the sense electrodes 132 and 133.
As further depicted in
Similarly, the sealing ring 145 (which has an inner edge 146) forms a seal around outer sidewalls of the sense electrodes 132 and 133 and the suspended graphene membrane 125. In addition, the sealing ring 145 partially overlaps the top surface of the suspended graphene membrane 125 and sense electrodes 132 and 133 along the outer sidewalls thereof. In particular, the inner edge 146 of the sealing ring 145 is disposed on top of the sense electrodes 132 and 133 and suspended graphene membrane 125, and extends past three sides of the sense electrodes 132 and 133, and two opposing sides of the suspended graphene membrane 125. The sealing layer 145 serves to prevent external gases from leaking into or out of the cavity 115 from under the side edges of the suspended graphene membrane 125 and from under the side edges of the sense electrodes 132 and 133.
Moreover, as shown in
More specifically, in the first mode of operation, as shown in
Once the reference Rref and test Rtest resistances are determined, the pressure of the test ambient Ptest can be determined by the following equation:
|Rtest−Rref|=α|Ptest−Pref| Equ. (1)
- wherein the value α represents the piezo-resistivity factor. In this mode of operation, the different forces of the applied pressure causes the suspended graphene membrane to deflect and stretch to different degrees, which cause changes in resistance of the thin suspended graphene membrane 125.
The use of graphene as an active electro-mechanical membrane of the pressure sensor device 100 discussed herein is advantageous for various reasons. For example, graphene is known to have a breaking strength 200 times greater than steel. In this regard, an active graphene membrane (e.g., the suspended graphene membrane 125) can be made very thin, down to one atomic layer. Moreover, with an extremely thin and strong active graphene membrane, the pressure sensor can operate with higher sensitivity as compared to an active Si membrane.
In another mode of operation, the optional control cell 210 can be used as a control measure to eliminate any measured change of resistance of the suspended graphene membrane 125 that is caused by chemical doping of a test gas. In particular, in the exemplary method discussed above, when the ambient changes from the reference ambient to the test ambient (test gas), the test gas can chemic ally dope the suspended graphene membrane 125, which adds to the change in resistance in addition to the change in resistance caused by the stretching/deflection of the suspended graphene membrane 125 due to the test ambient pressure. In this regard, the control cell 210 can be used to determine the change in resistance of the graphene membrane due to chemical doping and eliminate this factor.
More specifically, referring to
The insulating layer 110 may be formed using various types of dielectric or insulating materials such as oxides and nitrides, which are commonly used in VLSI fabrication including, but not limited to silicon nitride, silicon oxide, hafnium oxide, zirconium oxide, aluminum oxide, aluminum nitride, boron nitride or a combination of such materials. The insulating layer 110 may be formed using known deposition techniques. The insulating layer 110 may be a nitride layer or an oxide layer that is formed by growing oxide on silicon using well-known semiconductor fabrication techniques. For example, the insulating layer 110 may be formed of silicon nitride, silicon oxide, hafnium oxide, zirconium oxide, aluminum oxide, aluminum nitride, or boron nitride or a combination thereof. In a preferred embodiment, the insulating layer 110 has a thickness of about 90 nm or about 280 nm (or any suitable thickness to provide sufficient contrast for photolithographic etching of features on top of the insulating layer 110, as is understood by those of ordinary skill in the art).
After forming the graphene layer 310, the etch mask 320 is formed by depositing an etch mask material over the graphene layer 310 and patterning the etch mask material to form the etch mask 320 pattern. The etch mask 320 may be a photoresist mask that is formed using known photolithographic methods. The etch mask 220 is patterned to expose regions of the graphene layer 310 to be etched away, while covering regions of the graphene layer 310 that define the supported and suspended graphene membranes.
A next step in the fabrication process is to form the sense electrodes 130, 131, 132, and 133 as shown in
The sense electrodes can be formed of conductive materials including, but not limited to, titanium, palladium, gold, aluminum, poly silicon, TiN, TaN, tungsten, or a stack of one or more of such materials. For instance, the conductive layer 330 in
A next step in the fabrication process is to form the sealing rings 140 and 145 to seal the outer peripheral regions of the sense electrodes 130, 131, 132, 133 and the graphene membranes 120 and 125, as discussed above with reference to
It is to be understood that the invention is not limited to the particular materials, features, and processing steps shown and described herein. Modifications to the illustrative embodiments will become apparent to those of ordinary skill in the art. It should also be understood that the various layers and/or regions shown in the accompanying figures are not drawn to scale, and that one or more semiconductor layers and/or regions of a type commonly used in such integrated circuits may not be explicitly shown in a given figure for ease of explanation. Particularly with respect to processing steps, it is to be emphasized that the descriptions provided herein are not intended to encompass all of the processing steps that may be required to form a functional integrated semiconductor nano-device. Rather, certain processing steps that are commonly used in forming semiconductor devices, such as, for example, wet cleaning and annealing steps, are purposefully not described herein for economy of description. However, one of ordinary skill in the art will readily recognize those processing steps omitted from these generalized descriptions.
Although exemplary embodiments of the present invention have been described herein with reference to the accompanying figures, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be made therein by one skilled in the art without departing from the scope of the appended claims.
Claims
1. A method of forming a semiconductor pressure sensor device, comprising:
- forming an insulating layer on a semiconductor substrate;
- forming a recessed cavity in the insulating layer;
- forming a suspended graphene membrane on the insulating layer completely covering the recessed cavity, wherein the suspended graphene membrane has a thickness in a range of about one atomic layer to about ten atomic layers;
- forming a first sense electrode and a second sense electrode on the insulating layer on opposing sides of, and in contact with, the suspended graphene membrane;
- forming a sealing ring around outer sidewalls of the first and second sense electrodes and the suspended graphene membrane
- forming a supported graphene membrane on the insulating layer in a region adjacent to the first graphene membrane, wherein the supported graphene membrane is physically separate from the suspended graphene membrane, and wherein an entire surface area on one side of the supported graphene membrane is in direct contact with the insulating layer;
- forming a third sense electrode and a fourth sense electrode on the insulating layer on opposing sides of, and in contact with, the supported graphene membrane; and
- forming a second sealing ring around outer sidewalls of the third and fourth sense electrodes and the supported graphene membrane,
- wherein the suspended graphene membrane is a part of the semiconductor pressure sensor device that is configured to operate as a device cell for testing pressure of an ambient gas based on a change of resistance of the suspended graphene membrane caused by pressure applied on the suspended graphene membrane by the ambient gas, and
- wherein the supported graphene membrane is a part of the semiconductor pressure sensor device that is configured to operate as a control cell for determining an amount of change in resistance of the suspended graphene membrane due to chemical doping of the suspended graphene membrane from the ambient gas.
2. The method of claim 1, wherein the recessed cavity is filled with air.
3. The method of claim 1, wherein the recessed cavity contains a vacuum.
4. The method of claim 1, wherein the insulating layer comprises silicon nitride, silicon oxide, hafnium oxide, zirconium oxide, aluminum oxide, aluminum nitride, or boron nitride or a combination thereof.
5. The method of claim 1, wherein a width of the recessed cavity between the first and second sense electrodes is in a range of about 0.2 um to about 5.0 um.
6. The method of claim 1, wherein a depth of the recessed cavity is in a range of about 20 nm to about 300 nm.
7. The method of claim 1, wherein the sealing ring comprises a spin-on glass layer, a Hermetic seal, or a rubber seal.
8. The method of claim 1, wherein the supported graphene membrane has a thickness in a range of about one atomic layer to about ten atomic layers.
7409864 | August 12, 2008 | Yane et al. |
20050053525 | March 10, 2005 | Segal et al. |
20050212014 | September 29, 2005 | Horibe et al. |
20060063354 | March 23, 2006 | Fortin et al. |
20100140723 | June 10, 2010 | Kurtz et al. |
20120056161 | March 8, 2012 | Avouris et al. |
- Smith (“Strain Effects on Electrical Properties of Suspended Graphene” Master Thesis in Integrated Devices and Circuits Royal Institute of Technology (KTH), Available from: Dec. 20, 2011.
- Koenig et al. (“Ultrastrong adhesion of graphene membrane” Nature Nanotechnology 6, pp. 543-546, (2001) Published online Aug. 14, 2011.
- C. Lee et al, “Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene,” Science, Jul. 2008, pp. 385-388, vol. 321, No. 5887.
- A. Turchanin, “One Nanometer Thin Carbon Nanosheets with Tunable Conductivity and Stiffness,” Advanced Materials, Mar. 2009, pp. 1233-1237, vol. 21, No. 12.
- Y. Lee et al., “Wafer-Scale Synthesis and Transfer of Graphene Films,” Nano Letters, Feb. 2010, pp. 490-493, vol. 10, No. 2.
- O. Kanoun et al., “Potential of Carbon Nanotubes for Sensor Applications,” IEEE 5th International Multi-Conference on Systems, Signals and Devices (SSD), Jul. 2008, pp. 1-6.
- D. Pandey et al., “Graphene Based Sensor Development,” http://phys570x.wikispaces.com/file/view/proposal-report—graphene—sensor.pdf, Apr. 2009, 10 pages.
- I.W. Frank et al., “Mechanical Properties of Suspended Graphene Sheets,” Journal of Vacuum Science & Technology B, Microelectronics and Nanometer Structures, Nov./Dec. 2007, pp. 2558-2561, vol. 25, No. 6.
Type: Grant
Filed: Aug 31, 2012
Date of Patent: Oct 7, 2014
Patent Publication Number: 20130273682
Assignee: International Business Machines Corporation (Armonk, NY)
Inventors: Jin Cai (Cortlandt Manor, NY), Yanqing Wu (Ossining, NY), Wenjuan Zhu (Fishkill, NY)
Primary Examiner: Asok K Sarkar
Assistant Examiner: Dmitriy Yemelyanov
Application Number: 13/600,469
International Classification: H01L 21/00 (20060101); H01L 29/02 (20060101);